An unmanned aerial vehicle (UAV), which may also be referred to as an autonomous vehicle, is a vehicle capable of travel without a physically-present human operator on board. A UAV may operate in a remote-control mode, in an autonomous mode, or in a partially autonomous mode.
When a UAV operates in a remote-control mode, a pilot or driver that is at a remote location can control the UAV by commands that are sent to the UAV via a wireless link. When the UAV operates in autonomous mode, the UAV typically moves based on pre-programmed navigation waypoints, dynamic automation systems, or a combination of these. Further, some UAVs can operate in both a remote-control mode and an autonomous mode, and in some instances may do so simultaneously. For instance, a remote pilot or driver may wish to leave navigation to an autonomous system while manually performing another task, such as operating a mechanical system for picking up objects, as an example.
Position and orientation of the UAV should be known for a variety of reasons, for example, for maintaining the required flight path of the UAV, for avoidance of obstructions, avoidance of the flight path of the commercial aircraft, precise delivery of the payload, precise coverage of certain ground area when the UAV is used in telecommunication, etc. In practice, unmanned aerial vehicles (UAVs) typically carry a global positioning system (GPS)-based primary navigation system onboard to determine the UAV's location. For various reasons, however, the GPS-based navigation system may fail, rendering the UAV inoperable. For example, the GPS signal may be erroneous or too weak to be used by the UAV. Furthermore, the GPS equipment of the UAV may also fail, thus making the UAV, at a minimum, incapable of fulfilling its tasks, but possibly also dangerous to other air vehicles.
Accordingly, there remains a need for the systems and methods that precisely determine the location of the UAVs even when GPS signal is weak or erroneous, or when the GPS system of the UAV fails.